Art of cracking hydrocarbons



Jan. 6; 1931. E. c. HERTHEL ET AL 1,787,981

ART OF CRACKING HYDROCARBQNS Filed Jun 11, 1927 INVENTOR 6 i'l/jenc Cf/er M l I flarr L. Feller BY 5 5; W $2M ATTORNEYS Patented Jan. 6, 1931UNITED STATES PATENT OFFICE EUGENE C. HERTfiELQOF CHICAGO, ILLINOIS, ANDHARRY L PELZER, OF HIGHLAND, INDIANA, ASSIGNORS T0 SINCLAIR REFININGCOMPANY, OF NEW YORK, N. Y.,

CORPORATION OF MAINE ART OF CRACKING HYDROCARBONS Application filed June11,

This invention relates to improvements in the cracking of heavier andhigher boiling hydrocarbon oils, such as gas oil, to produce therefromlighter and lower-boiling hydrocarbon oils, such as gasoline andgasolinecontaining pressure distillates. This invention relatesparticularly to improvements in the operation and arrangement ofexternally heated pressure cracking stills, that is pressure crackingstills in which the heat for the cracking operation is supplied byheating gases passed externally over the heating surfaces of the stillfrom a firebox in which fuel is burned. The invention includesimprovements in both method and apparatus.

The products of the cracking reaction'inelude, in addition to thedesiredlighter and lower boiling hydrocarbon oils, asphaltic andpitch-like constituents which tend to deposit upon the heating surfacesof externally heated pressure'stills. Such deposits obstruct heattransfer and tend to cause extreme overheating because of thisobstruction of heat transfer, necessitating periodic shut down of thepressure still for cleaning, thus limit-ing the useful period ofoperation. -As the concentration of such asphaltic and pitch-likeconstituents in the charge of oil in the pressure still increases, thetendency toward deposition of such materials also increases. Thisinvention provides for reduction'in the concentration of asphaltic and"pitch-like constituentsin the oil in-contact with the heating surfacesof the still, and for tempering of the heating gases passing over theheating surfaces through which heat is transferred to that portion ofthe charge containing the greater concentration of such constituents bya corresponding absorption of heat from the heating gases by heatexchange with oil substantially free from such constituents and of acharacter such that the tendency toward the formation of suchconstituents is materially reduced, as well as for particularlyadvantageous treatment of relatively refractory stocks; thus providingimproved continuity of operation with accompanying increase in stillcapacity and in efficiency of operation.

According to the present invention, a body 1927. Serial No. 198,248.

of oil is maintained at a cracking temperature under pressure in avaporizing zone, the oil being heated to a cracking. temperature inheating tubes through which it is circulated from the body and back tothe body, and a bed of finely divided absorbent or filtering material ismaintained within the body of oil in the vaporizing zone so that thecirculating oil is caused to pass through it. Vapors taken over theheating tubes through which oil from the body in the vaporizing zone isrepeatedly circulated. The concentration of asphaltic or pitch-likematerials in the oil circulated and recirculated from the vaporizingzone through the first mentioned heating tubes and back to thevaporizing zone is thus reduced by the act-ion of the bed. of absorbentor filtering material. At the same time, the heating gases are temperedbefore they come in contact with these heating tubes over which theheating gases first pass. These separate heating tubes are thus exposedto the heating gases while at highest temperature, but the oilcirculated through these heating tubes is substantially free fromasphaltic or pitchlike constituents and, this reflux condensate beingrelatively refractory, the formation of asphaltic or pitch-likeconstituents in the oil circulated through the separate heating tubes isreduced or retarded while this relatively refractory stock is subjectedto particularly advantageous cracking conditions for further productionof .desired lighter and lower boiling hydrocarbon oils. The oil suppliedthereto advantageously is circulated but once or in a single'passthrough the separate heating tubes.

F ullers earth, or a similar absorbent earth A in the Cracking oeration, which appear to be relatively smal in amount as comparedmaterials, are also useful in carrying out the invention, but fullersearth is particularly eflicacions, apparently combining in itselfvaluable selective absorbent, desul hurizing and other properties whichfavora ly affect and benefit the pressure still operation. For example,fullers earth seems to have a selective affinity for the moreobjectionable as phaltic and pitch-like constituents formed by thecracking operation.

In addition to reflux'condensate, raw oil may also with advantage becirculated through the separate heating tubes arranged in advance ofthose through which oil is circulated and recirculated from thevaporizing zone. Such raw oil may be'supplied directly to the separateheating tubes in ad mixture with the returned reflux condensate,

or, .and this is a particularly advantageous method of operation, theraw oil, or part of it, may be introduced into the refluxing operationfor promoting or controlling the refluxing operation and for preheatingthe raw oil. Admixed reflux condensate and unvaporized raw oil ma thenbe supplied to the separate heating tn 5 from the refluxing operation.Additional raw oil may also be supplied directly to the charge of oilcirculating through the vaporizing zone, and part of the refluxcondensate, or admixed raw oil and refluxed condensate, from therefluxing operation may also be supplied directly to the body of oilcirculating through the vaporizing zone as required without first beingpassed through the separate heating tubes.

The present invention thus provides improved protection for all of theexternally heated heating surfaces of the pressure still. The heatingtubes with which the heating gases first contact and which accordinglyare exposed to the heating gases while at highest temperature areprotected. by circulation therethrough of relatively refractory stockand stock which is substantially free from asphaltic and pitch-likeconstituents formed in the cracking operation, the stock circulatedthrough these first heating tubes being either reflux condensate or amixture of reflux condensate and raw oil. The remaining heating tubesare protected in a dual manner; they are protected by the action of thebed of finely divided. absorbent or filtering material in reducing theconcentration of asphaltic and pitch-like constituents in the oilcirculating therethrough, and they are further protected by thetempering of the heating gases effected by heat absorption in the firstheating tubes. The. reflux condensate circulated through the firstheating tubes is also subjected to advantageous cracking conditions,this reflux condensate being relatively refr'ac tory with respect to thecracking conditions to which the body of oil circulated and recirculatedthrough the remaining' heating Referring to the drawings, the pressurestill illustrated comprises a bulk supply drum 1, a battery of heatingtubes 2 and circulating connections 3, 4 and 5 including a circulatingpump 6 arranged to provide for circulation of oil from the bulk supplydrum through the heating tubes 2 'and back to the bulk supply drum.Arranged in the bulk supply drumand below the normal liquid leveltherein is a bed 7 of finely divided absorbent o'r filtering material.This bed is supported on a suitable support 8 adapted to retain thefinely divided solid material but to permit free passage of oiltherethrough. The support may consist, for example, of one or morescreens arranged between perforated plates or between suitable gratings;The support 8 and the bed offinely divided solid material thereon arearranged in the bulk supply drum 1 extending entirely across the -bulksupply drum and between the circulat- 1ng connections 3 to thecirculating tubes 2 and the circulating connections 5 from the heatingtubes so that oil circulating and re- I furnace in the flue betweenthefirebox 10 and the heating tubes 2 so that heating gases from thefirebox must pass over these heating tubes 12 before contacting with theheating tubes 2. Further-to assist in tempering the heating gasespassing. over the heating tubes,

means for clrculating over the heating tubes a portion ofthelescaping'waste heating gases in admixture with fresh hot products of comoustionfrom the firebox may be provided, as shown at 13.

Arranged above the bulk supply ,drum 1 is a refluxtower 14. Vapors fromthe bulk supply drum enter the lower end of this reflux tower throughvapor line 15. Vapors remaininguncondensed escape from the upper end ofthis reflux tower through vapor line 16 to the condenser 17 arranged todischarge into the receiver 18. The distillate product is dischargedfrom the receiver 18 through the connection 19 and uncondensed vaporsand gases through the connection 20. The pressure in the'system may bemaintained and regulated by means of the valve 21 or by means ofsuitable valves arranged beyond the condenser or receiver. Refluxcondensate from the reflux tower 14 is conveyed to the reservoir 22through connection 23. A supplemental vaporline between the upper end ofthe reservoir 22 and a point in the reflux tower above the outlet forreflux condensate is provided at 24. From the reservoir 22, refluxcondensate is circulated through the heating tubes 12 by means ofconnection 25 or pump 26 and connection 27. The hot oil products fromthe heating tubes 12 are discharged into the bulk supply drum 1 throughconnections 28 and 5. Feed line 29 is provided for introducing raw oilinto the upper end of the reflux tower 14. Raw oil so introduced intothe reflux tower 14 passes to the reservoir 22 and continues inadmixture with the reflux condensate. Additional raw oil may be supplieddirectly to the heating tubes 12 through connection 30. An overflowconnection for reflux condensate, or reflux condensate and admixedunvaporized raw oil, in excess of that discharged through connection 23is provided at 31. Oil may also be discharged from the reservoir 22 intothe upper end of the circulating connection 3 through connection 32. Iffor any reason the supply of oil to the heating-tubes 12 from reservoir22 is insufficient, as in starting the operation, a part of therecirculating charge of oil in the pressure still may be suppliedthereto through connection 33, or other oil may be supplied throughconnection 30.

A tar line for discharging tar or pitch laden oil from the pressurestill during operation is provided at 34. A connection for.

pumping out and for initially charging the still is shown at 35. Oil forcooling and lubricating the bearings of the circulating pump 6 may besupplied through connection 36, or raw oil in excess of the amountrequired for cooling and lubricating the pump bearings may be suppliedto the recirculating still charge through this connection and forced inthrough the pump bearings.

The bulk supply drum 1, the reservoir 22, and the several hotconnections are all advantageously lagged or insulated to prevent orreduce heat loss. Where the refluxing operation is effected by heatexchange with raw oil, as inthe apparatus illustrated, it is alsoadvantageous to lag or insulate the reflux tower 14.

In starting operation, the still system 'is charged with oil andgradually brought to cracking conditions of temperature and pressure inthe usual manner. While the still is being brought to crackingconditions, or until an adequate supply of reflux condensate isavailable, a portion of the oil discharged recirculating through theheating tubes 2 will 0 in general be the temperature corresponding tothe. pressure used; but the oil circulating through the heating tubes 12may be superheated to a considerably higher temperature. For example, ifthe oil body in the bulk supply drum 1 is at a temperature in the neighborhood of 750 to 775 F., the hot oil products from the heating tubes 12as discharged through connection 28 may be at atemperature of from 775to upwards of 825 F. The refluxin operation may be controlled byregulated mtroduction of raw oil through connection 29; for example, thetemperature at which the vapors remaining uncondensed escape from theupper end of the reflux tower may be maintained at some appropriatepredetermined temperature b regulating the introduction of raw oil.Kdditional raw oil supplied to the operation may be introduced throughconnection 36 or in part through connection 36 or through connection 30or in part through connection 30. In a' pressure still of the typeillustrate in which the bulk supply drum 1 is adapted to contain anormal operating charge in the neighborhood of 10,000 gallons, the bedof finely divided solid material 7 may with advantage consist of fromfour to seven tons of fullers earth. It is advantageous to userelatively coarse earth, say from 15. to 30 mesh, although finer earthmay be used. The

tar line 34 is advantageously arranged, as

illustrated,'to discharge pitch-laden oil from the body-of oil in thebulk supply drum 1 from above the bed-of finely divided filtering orabsorbent material, although it may be the still charge.

the repeated passage of the circulating oil through the bed of absorbentor filtering material 7. This bed of filtering or absorbent material isentirely submer ed in and directly exposed ,to the body of oil in thebulk supply drum 1 so as to exert its maximum effect upon Theconcentration of asphaltic and pitch-like constituents in the charge ofoil circulating through the bulk supply drum 1 is further ;controlled bythe discharge of tar or pitch-laden oil through connection 34 inconjunction with the supply of raw oil to the operation. During theoperation, the oil circulated through the battery of heatin tubes 2 willnevertheless contain some asp altic and pitch-like constituents butthese heating tubes are further protected by the tempering of theheating gases effected by the heat absorption by the separate bank ofheatingtubes 12.

The heating gases including fresh hot products of combustion from thefirebox pass first over the separate bank of heating tubes 12 and thenover the battery of heating tubes 2 so that the reduction in temperatureof the heating gases as they pass over the heating tubes 12 reduces thetemperature of the heating gases as they contact with the heating tubes2. The separate bankof heating tubes 12 are protected by the circulationof oil substantially free from asphaltic and pitch-like constituentstherethrough, either reflux 'con densate from the reflux tower ,14 orsuch reflux condensate admixed with raw oil. 1 The relatively refractorycharacter of the reflux condensate, moreover, assists in furtherreducing or retarding the formation of as- .phaltic or pitch-likeconstituents in' the heating tubes 12, that is the heating tubessubjected to highest temperatures. 7

The hot oil products discharged from the separate bank of heating tubes12 may assist in heating, internally, the charge of oil in the bulksupply drum 1'. Where the hot 011 products are heated in the heatingtubes 12 to a temperature substantially higher than that prevailing inthe bulk suppl drum 1, the reduction of tem erature of t e hot oilproducts discharged om the separate'bank of heating tubes 12 as they areintroduced into the body of oil in the bulk supply drum 1 may alsoassist in arresting any tendency toward overcracking.

We claim:

1. An improved method of cracking hydrocarbon oils, which comprisescirculating .oil

from a body of oil in a vaporizing zone through heating tubes and backto the and heating it to a cracking temperature in the heating tub'es,maintaining a bed of fine- 1y divided solid absorbent material withinsaid body of oil so that the circulating oil-is caused to passtherethrough, taking off vapors from said vaporizing zone undersuperatmospher c pressure and subjecting'themto from a body of oil in avaporizing zone through heating tubes and back to the body and heatingit to a cracking temperature in the heating tubes, maintaining a bed'offinely divided solid material within said body of oil so that thecirculating oil is caused to pass therethrough, taking ofi vapors fromsaid vaporizing zone under superatmospheric pressure and subjecting themto a refluxing operation, introducing raw oil into direct contact withthe vapors in the-refluxing operation, circulating admixed refluxcondensate and unvaporized raw oil from said refluxing operation throughseparate heating tubes into said vaporizing zone, and passing heatinggases from afirebox in which fuel is burned for supplying heat to thecracking operation first over said separate heating tubes through whichadmixed reflux condensate and unvaporized raw oil is circulated andthenover the first mentioned heating tubes.

3. An improved method of cracking hydrocarbon oils-which comprisescirculating oil from a body of oil a vaporizing zone through heatingtubes and back to the body and heating it to a cracking temperature inthe heating tubes, maintaining a bed of finely divided solid materialwithin said body of oil so that the circulating oil is caused to passtherethrough, taking ofi vapors from said vaporizing zone undersuperatmoipheric uxing pressure and subjecting them'to a re operation,circulating reflux-condensate from vaporizing zone, and passing heatinggases from a firebox in which fuel is burned for supplying heat to thecracking operation first over said separate heating. tubes throughthrough heating tubes and bac to the body .and heating it to a crackingtemperature in the heating tubes, maintaining a bed of finely dividedsolid material within said body of oil so that the circulating oil iscaused to pass therethrough, taking off vapors from said vaporizing zoneunder superatmospheric pressure and subjecting them to a re-- saidrefluxing operation together with raw .oil through separate heatingtubes into said first over said separate heating tu fluxing operation,circulating reflux condensate from said refluxin operation throughseparate heating tubes 1nto said vaporizing zone, dischargingpitch-laden oil from thebody of oil in said vaporizing zone andsupplying raw oil, and passing heating gases from a firebox in whichfuel is burned for supplying heat to the crackin operation through whichreflux condensate is circulated and then over the first mentionedheating tubes.

5. An improved method of cracking hydrocarbon oils, which'comprisescirculating oil from a body of oil in a vaporizing zone through heatingtubes and back to the body and heating it to a. cracking temperature inthe heating tubes, maintaining a bed 1 of fullers earth within said bodyof oil so that the circulating oil is caused to pass therethrough,taking off vapors from said vaporiz'ing zone under superatmosphericpressure and subjecting them to a refluxing operation, recirculatingreflux condensate fromsaid refluxing operation through separate heatingtubes into said vaporizing zone, and passing heating gases from afirebox in which fuel is turning'reflux condensate from the refluxingoperation to said heating coil, maintaining a bed of finely dividedsolid material within said body of oil, circulating unvaporized oil insaid conversion chamber through the bed .of finely divided'solidmaterial and thereburned for supplying heat to the cracking oporationfirst over said separate heating tubes through which reflux condensateis circulated and theno-ver the first-mentioned heating tubes.

6. An improved apparatus for cracking hydrocarbon oils, com rising aheating furnace having a heating iiiie, a firebox connected to one endthereof and a stack flue to the other,

a bulk supply drum and a battery of heatingtubes arranged in the heatingflue' of the heating furnace and circulating connections for circulatingoil from the bulk supply drum through the heating tubes and back to thebulk supply drum, a bed of finely'divided s0l-.

id material arranged in the bulk supply drum below the normal liquidlevel therein and extending entirely across the bulksupply drum sbetween the circulating connection from thesaid heating tubes and thecirculating connecv tion to-the said heating tubes, a reflux tower and avapor line from the bulk supply drum to the reflux tower, a separatebank of heating tubes arrangedin the heating flue of the heating furnacebetween the firebox and thefirst mentioned bank of heating tubes, andcirculating connections forcirculating reflux condensate from saidreflux tower through said separate bank of heating tubes back to thebulk supply drum.

v 7. An improved method of cracking hydrocarbon oil which comprisespassing the oil through a heating co'ilwherein it is subjected to aconversion temperature, discharging the heated oil into an enlargedconversion chamber and maintaining a body of oil therein, taking oflvapors fromsaid conversion cham ber under superatmospheric pressure andsubjecting them to a refluxing operation, re-

